This invention relates generally to image processing methods and systems, and, more particularly to methods and systems for determining and correcting the orientation angle of an image.
When an image is scanned in order to obtain an electronic image, in many instances, the resulting electronic image is rotated (has an angular orientation different from that desired). This phenomenon can occur when a photographic image, text image, or a compound document is scanned. There are also situations of interest, such as automatic targeting and automated tracking, where, although an unintentional rotation is not introduced, the determination of the angular orientation of an object in the image is desired.
In view of the ubiquity of the problem in electronic image processing, a number of angular orientation detection methods have been proposed. Early angular orientation detection methods required the presence of text in the image. More recently, angular orientation detection methods have been described that require determining an edge in the image and determining, from that edge (or line), the orientation angle (see, for example, U.S. Pat. No. 5,901,253, “Image Processing System with Image Cropping and Skew Correction”, issued on May, 1999, and U.S. Pat. No. 5,528,387, “Electronic Image Registration for a Scanner”, issued on Jun. 18, 1996).
Methods that determine the orientation angle by finding straight lines or edges can encounter difficulties if the image is not rectangular or if the content of the image is rotated compared to the outline of the image. The latter example can be representative of the images obtained through address block location when the address is handwritten. For example, the method described in U.S. Pat. No. 5,901,253, detects multiple orientation angles when the image shape is oval. In that method, further processing is then necessary to determine the actual orientation angle of an image of oval shape.
Also, methods that determine the orientation angle by finding straight lines or edges are computationally intensive as can be inferred from the flow charts given in U.S. Pat. No. 5,901,253, U.S. Pat. No. 5,452,374, and U.S. Pat. No. 5,528,387. There is a need for a simple and robust method of determining the orientation angle of a scanned image or the angular orientation of an object in an image. There is also a need for a method that can be applied to images of different shapes and types.